1. Field of the Invention
The present invention relates to a starting and generating apparatus for an engine, which is adapted for starting an engine by using a rotator, as well as for generating electricity by driving the rotator at a constant rotational speed with the output of rotation of the engine which has been brought into an independently operated state after started by the rotator.
2. Description of the Related Art
Conventionally, in a large-sized aircraft, an air-turbine type starter utilizing compressed air has been predominantly used as an engine starter. For such an air-turbine type starter, it is necessary to provide an APU (Auxiliary Power Unit), or compressed-air pipe, valves and the like, between the engine and the related equipment located outside the aircraft. As a generator configured to be driven by axial force of the engine and generate electric power after the engine is started, an IDG (Integrated Drive Generator) type is predominantly used. This IDG type generator is configured to obtain a constant frequency by rotating the generator at a given rotational speed, irrespectively of the rotational speed of the engine, by using a continuously variable speed transmission. Alternatively, a VF (Variable Frequency) type generator, which generates a variable frequency without utilizing any transmission, is also prevalent. This VF type generator is configured to supply, at a site where the control of frequency is required, the electric power to each of the related electric equipments after controlling the frequency by using inverters or the like means which are dispersedly disposed. However, in the case of using such generators, it is necessary to provide the engine starter separately from the generator. Therefore, the use of such generators tends to increase the total weight and requires a relatively wide space, leading to increase of the cost. In addition, such an air-turbine starter is likely to malfunction. Especially, the compressed-air pipes increase the weight and require a considerably wide space for installment, thus raising the cost. Besides, in the case of employing the VF-type generator, it is necessary to provide additional equipment, such as the inverters or the like.
Meanwhile, for the aircraft engine, it has been attempted to reduce the weight by using a single motor for the engine starter as well as for the generator, i.e., by using the motor as the so-called starter/generator. In this case, it is necessary to generate considerably large driving torque by using such a starter/generator when starting the engine. However, a brushless synchronous generator, which is commonly known as the generator used for the aircraft, cannot generate such large starting torque when used as the motor. Meanwhile, a permanent magnet synchronous generator can generate such large starting torque, while the voltage cannot be well controlled. Therefore, such a permanent magnet synchronous generator should require a proper power converter (or starting inverter), leading to unwanted increase of the engine size.
To address such problems, Patent Document 1 discloses the aircraft engine configured to suppress the capacity of the power converter. In this engine, a main motor is first started by supplying electricity to the permanent magnet synchronous generator attached to the main motor via the power converter in order to drive the magnet synchronous generator. The rotation of the main motor is accelerated by connecting the power converter with the main motor, and the main motor is operated as a synchronous generator after the engine is started. Alternating-current electric power is supplied to this synchronous generator without allowing the electric power to be transmitted through the power converter. Thus, the capacity of the power converter can be suppressed. Patent Document 2 teaches another aircraft engine configured for first supplying the alternating-current electric power together with direct-current electric power to an exciting stator when the engine is started, while starting the engine by supplying another alternating-current electric power to the main motor. Then, the alternating-current electric power supplied to the exciting stator is reduced as the rotational speed of the engine is increased, so as to supply only the direct-current electric power to the exciting stator at a point of time the rotational speed of the engine reaches a given value. Thereby, the main motor is operated as the generator for outputting electric voltage. Patent Document 3 describes still another aircraft engine configured for first supplying the alternating-current electric power to the exciting stator when the engine is started, while starting the engine by supplying another alternating-current electric power to the main motor via the power converter. Then, the direct-current electric power is supplied to the exciting stator after the engine is started, thereby allowing the main motor to output the electric voltage.
Furthermore, Patent Document 4 discloses the starter/generator using the IDG, which is provided with a hydraulic transmission and configured for switching the operation of the rotator from the starter motor to the generator by utilizing two one-way clutches. Patent Document 5 describes another construction, which is provided with a continuously variable speed traction transmission and configured for switching the operation of the rotator from the starter motor to the generator by utilizing the one-way clutches. Patent Document 6 teaches still another construction provided with the continuously variable speed traction transmission and configured for driving the continuously variable speed transmission to serve, apparently, as a torque amplifier when the motor is started.
Patent Document 1: U.S. Pat. No. 4,481,459
Patent Document 2: U.S. Pat. No. 5,493,200
Patent Document 3: JP 2005-98296 A
Patent Document 4: U.S. Pat. No. 4,315,442
Patent Document 5: U.K. Pat. No. 1,199,145
Patent Document 6: JP 2008-38902 A
However, each of the aircraft engines respectively disclosed in the above Patent Documents 1 to 3 is configured for starting the engine with a lower output of the motor, and hence requires the power converter in order to obtain desired starting torque. Therefore, the overall size of the apparatus should be enlarged, leading to significant increase of the cost. Additionally, each of the constructions respectively described in the Patent Documents 4 and 5 uses the plurality of one-way clutches in order to switch the operation of the rotator from the starter to the generator, resulting in a rather complicated structure. Furthermore, either one of the one-way clutches undergoes slipping in its non-operated state so that the operational efficiency and reliability of the engine are affected by such slipping. In addition, the construction disclosed in the Patent Document 6 is designed to start the motor while it is connected with the engine, thus imposing a considerably great load on the motor when it is started. Accordingly, this construction should employ such a large-sized motor that can output considerably large starting torque or use a proper additional power converter.